Reactivity calculation in the frequency domain for BWR stability codes

This paper deals with the problem of computing the feedback reactivity in the frequency domain codes as the LAPUR code. First, we explain how to calculate the feedback reactivity in the frequency domain using slab-geometry (1D) kinetics, also we show how to perform the coupling of the 1D kinetics with the thermal–hydraulic part of the LAPUR code in order to obtain the density to reactivity feedback coefficients, the power to reactivity feedback coefficients and the inlet temperature to reactivity feedback coefficients for the different channels. Also we explain how to solve the lambda eigenvalue equation in the frequency domain by the spectral nodal method and the comparison between the reactivity obtained by solving the eigenvalue equation in the frequency domain and the reactivity obtained from first order perturbation theory. Because LAPUR works in the linear regime, it is assumed that in general the perturbations are small. There is also a section devoted to the reactivity weighting factors used to couple the reactivity contribution from the different channels to the reactivity of the entire reactor core in point kinetics and 1D kinetics. Also we display a comparison of the reactivity obtained using point kinetics and 1D kinetics for the different kind of perturbations and we check the consistency of the results.